1. Field of the Invention
This invention relates to the field of remote control and more particularly, to an apparatus and method for remotely controlling a plurality of devices by means of radio frequency signals. The invention includes a number of novel security features to prevent unauthorized usage.
2. Discussion of the Prior Art
The use of radio frequency (rf) signals for the remote control of equipment is well known. For example, most automatic garage door openers employ low-power rf transmitters to open or close the garage door from within an approaching or departing vehicle. Children's remote controlled cars, trucks, boats and airplanes are also popular. However, most remote control systems have very little inherent security since the radio frequency spectrum is open to eavesdropping with both simple and elaborate receivers. Even digitally encoded control messages may be readily intercepted and these same messages may be rebroadcast by an unauthorized "intruder" at will. It is often easy for an intruder to correlate an intercepted digital message with the observation of a controlled activity and then for the intruder to replicate the desired controlled activity at will.
Most remote control devices of the prior art are configured for the control of a single device. If multiple devices must be controlled, multiple remote control channels and associated hardware (i.e., receivers, antennas, etc.) are generally required. The use of multiple rf channels makes the interception task of an intruder relatively simple since individual remote control tasks are more easily correlated with individual, identifiable rf signals. The present invention overcomes this problem by utilizing a single, primary rf channel (i.e., frequency) for the control of multiple devices. A transceiver usually located proximate the device(s) to be controlled receives remote control commands over a primary rf signal. The transceiver, in turn, decodes, authenticates, modifies, and rebroadcasts the remote control commands to individual devices using one or more low-power transmitters. The rebroadcast signal are at a different frequency than the primary rf signal. In addition, random time delays may be introduced before the rebroadcast to further disassociate the rebroadcast signal from the primary signal. Other security features are also included to make the task of interception of control signals extremely difficult.
Many attempts have been made to remotely control multiple devices. U.S. Pat. No. 3,735,412 for Remote Control Systems; issued May 22, 1973 to Roy Kampmeyer, teaches a simple, self-powered rf transmitter and receiver combination for use in a security system. The operating frequency is in the commercial fm band (88-109 MHZ) and the receiver output has only a simple relay contact. The system differs significantly from the system of the present invention. First, no attempt is made to keep the operating frequency secret. No transceiver employing a secondary frequency for rebroadcasting control information is employed. In addition, there is no attempt to encode a digital message packet, or to transmit only partial control information. Finally, unlike the inventive system, the Kampmeyer system is only capable of controlling a single device.
The problem of controlling multiple devices is addressed in U.S. Pat. No. 3,835,454 for Plural Channel Fm Remote Control System; issued Sep. 10, 1974 to Joseph Palmieri, et al. Palmieri, et al. teach a system for remotely controlling multiple servo units by using multiple, discreet transmission frequencies. In contradistinction, the system of the present invention features the use of a single transmission frequency and the encoding of a digital message including both address and control information to allow control of multiple, diverse remote devices. The Palmieri, et al. system controls only a single type of remote device, namely a servo unit. In addition, unlike the inventive system, no security features are disclosed.
U.S. Pat. No. 4,355,309 for Radio Frequency Controlled Light System; issued Oct. 19, 1982 to Robert M. Hughey, et al. teaches a system for the remote control of plural lights. The system operates at a frequency in the 320-360 MHZ range and features a digitally encoded device address. Plural receivers are set to one of several possible address codes so that each receiver responds only to transmissions intended for it. Complete control information is transmitted. The Hughey, et al. system also differs significantly from the inventive system. No transceiver is employed. No secondary, time delayed signal is utilized, and none of the other security features of the instant invention are present.
U.S. Pat. No. 4,454,509 for Apparatus for Addressably Controlling Remote Units; issued Jun. 12, 1984, to James A Buennagel, et al. uses a central message generation site and transmitter to send tone-encoded messages to a plurality of receivers. Upon command, each receiver may connect or disconnect an electrical load from the electrical power distribution network. In contradistinction, the inventive system utilizes a wireless command converter (transceiver) to rebroadcast a digitally encoded message packet on a different frequency. Also, elaborate security precautions at the central control center of the inventive system are missing from the Buennagel, et al. system.
Another attempt to provide remote control of multiple devices is disclosed in Telephone Operated Heating, Ventilating And/or Air Conditioning, the subject of U.S. Pat. No. 5,386,461, issued Jan. 31, 1995 to Richard R. Gedney. Gedney teaches a system for intercepting dual tone multiple frequency (DTMF) signal sent over a regular telephone line. Tones are decoded and utilized to activate a switch to provide on/off control of an electrical load. In an alternate embodiment, Gedney teaches the use of a low-power rf link between the tone decoding apparatus near a telephone line, and a thermostat in a remote location within the building. Specific tone sequences are used to set the thermostat to a desired temperature. The system of the present invention differs in that no telephone line is required for operation. In addition, the inventive system may be used to control a plurality of devices as opposed to the single heating, ventilating, air conditioning (HVAC) device described by Gedney. The inventive system utilizes significantly more secure encoding than is possible with simple, DTMF-based control systems. Also absent from the Gedney system is any provision for the authentication of a control signal. In contradistinction, the present invention features elaborate provisions to insure that only authorized control messages may be issued.
Another telephone-based control system, is described in U.S. Pat. No. 5,434,973 for Microcontroller for Providing Remote Control of Electrical Switches, issued Jul. 18, 1995 to Chao-Cheng Lu. Lu teaches a system for conveniently controlling multiple electrical loads within the confines of an area such as a house. Load switching is initiated at a local keyboard, although activation by means of telephone, cellular telephone, or computer network using conventional DTMF technology is also taught. Unlike the system of the present invention, no security is provided in the Lu system. Neither is the control of the system by means of a rf link (other than the cellular phone line) per se taught. In addition, Lu does not teach the use of a low power, secondary rf transmitter for the control of multiple loads within the structure.
It is, therefor, an object of the present invention to provide a radio frequency-based, remote control system for a plurality of diverse devices.
It is another object of the invention to provide control only from a central location.
It is a further object of the invention to provide a multiplicity of security features to prevent unauthorized control of any of the remotely-controlled devices.
It is still a further object of the invention to utilize wireless command converters (transceivers) which receive a partial or incomplete control message packet on a first frequency, authenticate the message packet and then form a new, complete message packet for re-transmission at a different frequency.
It is an additional object of the invention that the wireless command converter introduce a random time delay between reception of a message packet and rebroadcast of a new, complete message packet.
It is a further object of the invention to occasionally transmits spirrous, dummy control message packets.